As soon as you enable the webserver, it costs at least 200kB memory on the MMC flash card. Simple userdefined webpages seems to add very little to the memory requirement. The used memory only counts against the available MMC Load memory, not the S7 CPUs work memory. I have no experience with more complex webpages, or pages with graphics.
Enabling the webserver immediately grants access to some useful goodies, such as the diagnostics buffer. Thus, the enduser can diagnose the PLC without having STEP7 or a special HMI made for it.
Creating VAT tables is as simple as ticking an option in the VAT property dialog. The values in the VAT will be view-only.
So far I have managed to create a simple user-defined webpage with a table of tags that the user can modify. This complements the VAT tables, where the user can only view not modify the values.
I used the sample project to generate the HTML code. As long as you just make some tables with variables, it is not so difficult.
There is the possibility to have multiple languages. Also for the user-defined web-pages. But I think that it requires a lot of work to maintain.
Dont know if non-latin fonts (cyrillic, chinese, etc.) are supported somehow.
I have decided to only support english.
It is highly recommended to protect the user-defined webpages with a password. There is no structured user system. You define one or several users in the CPUs HW configuration. And these users can be granted access or gets no access. The configuration is fixed. You cannot create, modify or delete users, and the includes the passwords. So dont reveal the password to everyone !
A tip: define the user called "everybody" without password. If noone logs in, this will allow access to the user-defined webpages, but with view-only.
A small irritation: If no user with modify access is logged in, and an attempt to modify a value is done, then the modified values will be discarded, but with no notification or warning message.
One of the settings I have created is a command to write the modified values to the MMC card via SFC84 WRIT_DBL. This means that values can be modified, and also saved to non-volatile memory.
So far my conclusion is that the user-defined web-pages are quite useful for smaller simple "headless" application, where you still like to have some possibility to diagnose, observe values and change the odd parameter.